Because the white vote is now predominantly tribal in nature so people who always vote Labour do so and those who vote Tory do the same. Ken is banking on the fact that a lot of white voters in zones 4,5 & 6 essentially voted against him rather than a definite vote for Boris (lets be honest any sane person would have voted for a dyslexic chimp last time around if it meant getting Livingston out of office) so the turn out might not be so high next time around in those zones.

So if he can corner the minority votes in the inner zones it gives him far more of a fighting chance.

Its why Boris is essentially fighting this election on an anti-Ken basis again and perhaps why having Ken running again was not such a good idea. Boris has, by and large, done what he said he would do and I dont guage to much anti-Boris sentiment about but its a potential indifference which could hurt him rather than any sort of genuine desire to get rid of him. Boris has to make this an anti-Ken vote election. Anybody else and it would have been different.

But who knows. From what I understand the polling of a few months ago was showing that Boris would walk it where as recently its all been going Kens way. Hence the attacks over tax (which has surprised me with Livingstone because its a silly and unnessary mistake to make especially given the source of much of that income and whilst I loathe the man and all that he stands for with a passion I cannot fault his political 'nous' which seems to have let him down this time) and no doubt some other bits and pieces to come.

Well London is said to be predominantly Labour so if the so called "white vote" was as tribal as you say, Livingstone would be a dead cert.

Personally I think Johnson is an utter fraud who has done f-all for London and I would love to see him booted out of public office permanently. His team have tried to focus on Livingstone's tax affairs - which are obviously perfectly in order - because their candidate hasn't come up with any policies worth shouting about.